Heat pumps are not a new technology; the principles underlying their operation were described by Lord Kelvin in the 1850s. On the wall of the boiler room of the Pimlico District Heating Scheme you will find a Times article from the 1950s proposing a heat pump as a replacement for the then common open coal fire.
But while they are common on the Continent, their uptake in the UK has been low, with cheap gas from the North Sea displacing most other domestic heating sources from the 1970s onward.
In basic terms, heat pumps work by extracting heat from the ground or air with a refrigerant and concentrating it into a much higher temperature by pressurising the refrigerant and running it through a heat exchanger. This is the same mechanism as a fridge but in reverse, keeping the desired space heated rather than cooled.
Low carbon heat
Now that the full cost of burning fossil fuels is apparent, heat pumps are on the march again. Their unique ability to supply three to four units of heat for every one unit of electricity consumed makes them much more efficient than ordinary electric heaters, and an ideal heating method in a world where the cost of gas-related carbon emissions is simply too high. Any heat pump that produces over 2.3 units of heat for every unit of electricity already has lower carbon emissions than a gas boiler. In the future, a decarbonised electricity system coupled with heat pumps will allow us to heat our homes with very low associated carbon emissions.
Unfortunately, we’ve become used to boilers we can switch off and switch on whenever we need them, and heat pumps don’t work quite like that. They can deliver the same comfort and amount of heat gas boilers can (and potentially for less money per unit of heat), but they require a bit more planning. You can’t just switch a heat pump on when you get in from work and expect it to deliver heat instantly, not without severely reducing its efficiency. Because heat pumps are more efficient when their output temperature is lower, it can be more cost-effective to run them all the time, as a room can be kept warm either by lower temperatures all the time or higher temperatures for a limited number of hours. This can seem counter-intuitive when you’re used to switching off the heating when there’s no-one in the house.
Performing below par
As a result, the performance of heat pumps in the UK has been mixed. Alongside some poorly performed installations, a lack of consumer education has led to heat pumps being treated by their owners as gas boilers, leading to them producing heat at very low efficiency levels and consequently causing bills to skyrocket. A range of projects have tried to understand the way in which consumers engage with heat pumps, and found some very odd things. For every two houses using their heat pump properly, there’s one in which the owner has taken to going out into their garden and switching their heat pump on and off at the socket.
There are at least two solutions to this problem. The first is a straightforward requirement that anyone installing a heat pump is required to fully train the customer in how to properly programme their heating system to deliver heat when they want it. Unfortunately, education alone doesn’t guarantee a customer won’t revert back to their old way of operating their heating device – and will blame the heat pump when the bill comes in.
The second solution being put forward by some manufacturers is to simply design the customer out of the equation. Instead of the heat pump being programmed directly, the device learns to anticipate when the householder requires heat, and supplies it accordingly. This wouldn’t prevent people switching their heat pump on and off at the socket, but would perhaps forestall them thinking they needed to. In some commercial schemes, such as those in supermarkets, companies had found that staff were arriving in the morning, feeling cold, and attempting to switch the heat pump on, even though it was already lined up to deliver the scheduled heat. To accommodate this some models include a fan which switches on when staff attempt to interact with the device, but doesn’t actually deliver any heat. This gave staff the impression the device was switched on without causing additional running costs, while the pump still delivers the appropriate amount of heat.
Regardless of the eventual solution, it’s clear that in order to make heat pumps a viable alternative to gas boilers, a simple and easy to understand interface for them is necessary. It’s a great shame that Steve Jobs died before he could bring us the iPump.